Electronic devices, such as integrated circuit devices having an integrated circuit unit and a lead frame which are sealed within a protective enclosure, find wide use in products including consumer electronics, household appliances, computers, automobiles, robotics, telecommunications, and military equipment. The IC unit may be an integrated circuit on a chip or it may be a module, a hybrid integrated circuit (HIC) having one or more chips, other electronic components and circuitry on a plastic or ceramic support base. The IC devices are sealed within an enclosure such as a metal cap, ceramic shell, or plastic molding in order to protect the device from the environment, including mechanical and chemical damage. Molded plastic packaging of the electronic devices plays a major role in the microelectronics industry. Plastic packages are less expensive than other types of packaging options, such as ceramic and/or metal packaging, and provide performance and reliability that make them acceptable in a major fraction of worldwide electronic device packaging. A means to electrically interconnect the IC device to circuitry external of the package conventionally types the form of a lead frame. The lead frame is formed from an electrically conductive material, such as copper alloy or an iron-nickel alloy, by stamping or etching a metal blank into a plurality of lead fingers defining a central area in which the IC unit is mounted. The central area may include a paddle on which the IC unit is mounted, or may include an aperture in which the electronic device is mounted. Contact pads on an IC unit are typically connected to the leads of the lead frame by means of wires or tapes. Alternatively, ends of the leads may be soldered or conductive adhesive may be used to contact the pads.
After the IC unit is electrically connected to the leads of the lead frame, the assembly is encapsulated in a plastic molding compound with end portions of leads projecting beyond the edge of the encapsulant. The ends of the leads are then formed into different configurations. In FIGS. 4, 5 and 6 are shown typical prior art devices 40, 50 and 60, respectively, with leads having so-called "gull wing", "J" or "butt"-configuration, respectively, for surface mounting the devices onto circuit boards.
The packages may be dual-in-line package (DIP) and quad (or chip carrier) package. In the DIP, leads extend in straight lines from two edges of the formed body. When the number of leads becomes high, such as exceeding 48, a DIP configuration becomes impractical and wasteful of circuit board area. Quads, packages with leads on all four sides, are preferable for these higher lead count devices.
Manufacturing (e.g., encapsulation and lead shaping) and assembly (e.g., handling, placement and soldering) operations can distort the leads of the encapsulated devices resulting in an improper connection of the leads to contacts or pads upon the circuit interconnection boards. Conventionally, electrical connection and bonding of the leads to the contacts on the interconnection board is accomplished by soldering. However, the shape of the end portions of leads of such prior art shaped leads as are shown in FIGS. 4, 5 and 6, presents a small contacting area for establishing an electrical contact between the leads and the contacts on the interconnection board and will depend, primarily, on the solder connection between the leads and the conductors. A distorted configuration of at least some of the leads e.g., due to manufacturing and handling operations, could result in misalignment of contacting areas of the leads with respect to the contacts on the interconnection board, which, in turn, could result in a faulty electrical and mechanical connection. These problems are expected to be aggravated by industry trends toward thinner leads (e.g., 5-10 mil), closer spacing (pitch) between the leads (e.g., 5-10 mil) and smaller footprint combined with greater size of the devices, to accommodate higher number of leads on the device perimeter. Thus, there is a need for a packaging design which would eliminate or at least reduce these problems.